The present invention relates to an exhaust gas recirculation system for an internal combustion engine.
Conventionally, exhaust gas recirculation in an internal combustion engine for automobiles for the purpose of reducing emission of NOx in the exhaust gases is not performed when the engine is operated in the cold state, so as to avoid deterioration of drivability of the automobile, and is performed only when the engine has been warmed up. However, operation of the engine in the cold state with no exhaust gas recirculation is not desirable, in view of the high emission of NOx in the exhaust gases. In this connection, I contemplate that it is possible to perform exhaust gas recirculation in the cold state operation of the engine, and that it is possible to accomplish an effective reduction of NOx emission while ensuring desirable drivability of the automobile by employing, in the cold state operation of the engine, a non-zero rate of exhaust gas recirculation which is lower than the normal rate of exhaust gas recirculation adopted in the warmed up operation of the engine.